I have had terrible luck with 1-piece
oil pan gaskets over the years and have tried all brands,maybe it's just me, but all have leaked and some have poured..........I switched back to the standard cork gasket/rubber seals and have had great success in the "no leaks" department......same for valve cover gaskets.......
One thing I do that I think helps is with the block upside down on the engine stand,I clean the
oil pan rail very good with brake cleaner on a shop rag and let it dry, them smear a thin coat of blue RTV on the rail and put the cork gasket on and press it down in place and let it dry completely before installing the
oil pan.....that way I'm pretty sure it will not move/shift when I tighten the oil pan bolts.............same for valve covers,cept I RTV them to the valve cover itself.......
hope this helps....
David